Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.53	5.357%	$88.0047	$88.00	$88.00	$88.00
Purchase #2	$231.77	8.524%	$251.5261	$251.53	$251.55	$251.50
Purchase #3	$54.33	13.266%	$61.5374	$61.54	$61.55	$61.50
Purchase #4	$82.93	3.368%	$85.7231	$85.72	$85.70	$85.70
Purchase #5	$18.30	11.642%	$20.4305	$20.43	$20.45	$20.40
Purchase #6	$250.88	8.347%	$271.821	$271.82	$271.80	$271.80
Purchase #7	$192.93	12.379%	$216.8128	$216.81	$216.80	$216.80
7 purchase totals =	$914.67		$995.8556	$995.85	$995.85	$995.70